The development of insecticide resistance in a wide range of important insect pest species poses a serious challenge to effective crop protection, creating an urgent need for alternative control strategies. The problem is exemplified in the UK by recent difficulties in controlling aphids and globally by the intensive use of chemicals in attempts to control whitefly.
Pesticide resistance is often due to the enhancement of metabolic enzyme systems within the insect, particularly non-specific esterases and microsomal oxidases. These enzymes are present in insects to enable them to metabolise plant xenobiotics, but selection pressure from pesticides can result in greatly enhanced activity and insecticide resistance. It is known that inhibitors of these enzyme systems (insecticide synergists) can result in increased potency of insecticides. If such synergists are allowed sufficient time to inhibit these enzymes fully (temporal synergism) then the sensitivity of insect pests to pesticides can be increased by several orders of magnitude (Moores et al., 2005; Young et al., 2005; 2006; Bingham et al., 2007).
A number of natural and synthetic compounds induce effective plant resistance (including natural xenobiotics) by acting at specific points in plant defence pathways; BABA (β-amino butyric acid) and cis-jasmone are two examples of such chemicals. BABA, a non-protein amino acid is a potent inducer of resistance to plant pathogens, including viruses, bacteria, fungi and nematodes. Recent research at Imperial College has revealed that BABA also enhances plant resistance to insect pests, including aphids and Lepidoptera. Aphids on BABA-treated plants show very poor growth and survival (Hodge et al., 2005; 2006). Unlike other chemical inducers, BABA does not directly activate the plant's natural defence arsenal and therefore does not impose yield drag on crops. Instead, BABA conditions the plant for a faster and stronger activation of defence responses once attack by pest or pathogen has started, a process known as ‘priming’. The broad-spectrum protection conferred by BABA is effective against a wide range of pest and pathogen species, and operates in crop plants from many botanical families, making BABA a compound of enormous potential.
cis-Jasmone is a volatile plant activator involved with plant resistance (Birkett et al., 2000). Its activity was first discovered at Rothamsted Research when components of blackcurrant volatiles that repelled the summer form of lettuce aphid, Nasonovia ribisnigri, were being identified. Since then, cis-jasmone has been found to have more intricate effects on interactions between pest insects and crop plants. cis-jasmone may also act as an external signal, alerting recipient plants when their neighbours are being damaged by phytophagous insects and thereby enabling them to prepare their own defences prior to insect attack (Chamberlain et al., 2000, Pickett & Poppy 2001). The practical use of cis-jasmone initially focused on the interaction between the grain aphid Sitobion avenae and wheat, Triticum aestivum. Wheat plants sprayed with low levels of cis-jasmone as an aqueous emulsion were found to be less attractive to aphids, but more attractive to their parasitoids in laboratory bioassays. In the field, similarly treated plants had lower aphid infestations (Bruce et al., 2003). See also WO01/41568, EP Patent 1235483, and U.S. Pat. No. 6,890,525, herein incorporated by reference.
Examples of crop pests for which various treatments have been attempted include, but are not limited to, Myzus persicae, the peach-potato aphid. This is an important polyphagous insect pest of many commercial crops. One such crop is sweet pepper, Capsicum annuum, grown under glass, of which M. persicae is the most important vector of viral disease. Current control measures include the application of an aphicide or the use of biological control agents, particularly aphid parasitoids. The effect of the plant activator cis-jasmone as a switch to induce expression of defence-related biosynthetic pathways in sweet peppers, so as to reduce aphid colonisation and increase foraging efficiency of aphid parasitoids under glass, has been shown to be effective (Dewhirst, 2007).
Bemisia tabaci, the tobacco whitefly, is another globally important insect pest. In particular, the B&Q-biotypes are extremely invasive and resistant to many conventional insecticides. The host range consists of over 500 species in 74 families, covering almost all major agricultural systems, from cotton and vegetable field crops to ornamentals (Gunning et al., 1998). The tobacco whitefly has not been tested with cis-jasmone previously.
WO01/00026 discloses a tripartite composition for pest control comprising (a) a plant essential oil; (b) an enzyme inhibitor and (c) a synergist.